Familial adenomatous polyposis (FAP) is an inherited condition in which numerous adenomatous polyps form mainly in the epithelium of the large intestine. While these polyps start out benign, malignant transformation into colon cancer occurs when left untreated. The APC gene is a tumor suppressor gene that is located on band 5q21. Its function is not completely understood but has been shown to play a part in metaphase chromosome alignment.Normal APC protein promotes apoptosis in colonic cells. Its most important function may be to sequester the growth stimulatory effects of b-catenin, a protein that transcriptionally activates growth-associated genes in conjunction with tissue-coding factors. Mutations of the APC gene result in a truncated/nonfunctional protein. The resultant loss of APC function prevents apoptosis and allows b-catenin to accumulate intracellularly and to stimulate cell growth with the consequent development of adenomas Ileal pouch-anal anastomosis (J-pouch) surgery.